1. Field of the Invention
The present invention relates generally to a slicing machine equipped with a rotatable, flat, circular, ringed blade member having an internal cutting edge at an internal circumferential periphery thereof, wherein the internal cutting edge slices a workpiece made of semiconductor ingot or the like material to produce a wafer. More specifically, the present invention relates to a method and a device for detecting the flexure for use with this type of slicing machine and also to a flexure control device.
2. Description of the Prior Art
A slicing mechanism of such slicing machines is generally characterized in that a workpiece is placed in a central hole of a flat, circular, ringed blade member so as to slightly cross over the internal cutting edge in an axial direction of the blade member, and is shifted against the internal cutting edge in a radial direction of the blade member rotating to produce a wafer. Such a slicing machine is likely to cause a flexure of the blade member during cutting operation. This inherence of this kind of slicing machine may induce deterioration of machining accuracy due to undesirable flexure. To compensate the deterioration in the machining accuracy, detection of flexure has been conventionally attempted in various ways as shown in, for example, Unexamined Japanese Utility Model Publication No. 62-70904, Unexamined Japanese Patent Publication No. 1-182015.
FIG. 14 shows one of these conventional techniques for detecting the flexure. In the drawing, a flexure detecting sensor 29 is provided near a shifting zone C, along which a workpiece 30 moves in a direction of an arrow A, as close as possible without overlapping with this shifting zone C. This shifting zone C ranges from an inlet side P1 to an outlet side P2 of an internal cutting edge 11 of the blade member 10 in its widthwise direction. The flexure detecting sensor 29 is close to the inlet side P1, i.e., an upstream side of a rotational direction B of a flat, circular, ringed blade member 10. On the basis of a flexure amount detected by the flexure detecting sensor 29, an adjustment on overall flexure of the blade member 10 is performed in the axial direction of the blade member 10.
During slicing operation, contact between the flat, circular, ringed blade member 10 and the workpiece 30 to be sliced is longest at a midway point P3 of the shifting zone C. In other words, flexure occurring in this midway point P3 causes adverse affection to machining accuracy of the workpiece 30 most seriously. It is, thus, desirable to locate the above flexure detecting sensor 29 at a position closer to the shifting zone C, especially to a position corresponding to the midway point P3. However, interference between the flexure detecting sensor 29 and the workpiece 30 must be avoided. Accordingly, the position where the flexure detecting sensor 29 is installed needs to be out of the shifting zone C being offset far away from the midway point P3, as shown in FIG. 14. This inevitable offset from the midway point P3 results in a problem that an overall adjustment on flexure of the blade member 10 cannot be done accurately or properly.
To solve this problem, there has been recently proposed a detecting technique, as disclosed in Unexamined Japanese Patent Publication No. 4-138210. According to this prior art, a flexure detecting sensor of eddy current type is disposed at a position confronting with the front end surface of a workpiece to be machined so as to detect a flexure amount of the central portion of the workpiece through a wafer produced being cut off from the workpiece. This detecting technique is advantageous in that the flexure detecting sensor can be disposed near the central portion of the workpiece because interference between the workpiece and the flexure detecting sensor can be surely avoided.
However, a problem of this type detecting technique resides in that the flexure amount is indirectly detected. More specifically, the wafer is interposed between the workpiece and the flexure detecting sensor; therefore, the flexure amount detected will reflect a significant amount of affection by the wafer. Some of the workpieces have electric resistances comparable with conductors. Furthermore, the thickness or size of the wafer produced from the workpiece is not always constant, rather varies depending on slicing condition. Due to such size dispersion of the wafer, it is normally difficult to accurately detect the flexure amount of the blade member on the basis of the value measured by the flexure detecting sensor.